Tiffany is 3 times as old as Emily and is also 10 years older than Emily. How old is Emily?
Explanation: We can use the given information to write down two equations that describe the ages of Tiffany and Emily. Let Tiffany's current age be $t$ and Emily's current age be $e$ $t = 3e$ $t = e + 10$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $e$ , and both of our equations have $t$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $3e$ $-$ $ (e + 10)$ which combines the information about $e$ from both of our original equations. Solving for $e$ , we get: $2 e = 10$ $e = 5$.